This invention relates to dialysis machines, and more particularly, to deairing systems for use in dialysis machines of the type known as bedside consoles.
In dialysis, a patient's blood and dialysis solution flow through a dialyzer which includes a semipermeable membrane for separating the blood and the dialysis solution. Impurities from the blood cross the membrane and enter the dialysis solution for disposal.
In some dialyzers the dialysis solution is drawn through the dialyzer under a negative pressure (i.e., below atmospheric pressure). The reduction of the pressure on the dialysis solution to below atmospheric pressure allows dissolved gas to come out of solution and form bubbles. If such bubbles enter the dialyzer, they can undesirably impair the efficiency and operation of the dialyzer.
Degassing or deairing systems are known for removing gas from the dialysis solution prior to dialysis. In U.S. Pat. No. 3,598,727 there is shown a central delivery system in which the dialysis solution is prepared and degassed at a central location and then delivered to multiple remote stations. The remote stations means. includes a dialyzer and an apparatus known as a "beside console" which monitors and controls the operation of the dialyzer. A venturi is provided at the bedside console for drawing the dialysis solution through the dialyzer under a negative pressure.
The degassing portion of this system includes: a pump, a restriction, and an atmospheric pressure debubbling tank, all of which are located at the central station. No degassing is provided at the bedside console and the debubbling tank is operated only at atmospheric pressure.
It is one object of this invention to provide an economical and efficient degassing system for use in a bedside console.
Another type of dialysis machine is shown in U.S. Pat. No. 3,626,670. In that machine there is provided a single pump positioned downstream of the dialyzer for drawing solution therethrough and a chamber upstream of the dialyzer for deairing. The dialysis solution flows through the chamber and the pump applies a negative pressure to the chamber for deairing the solution. Thus, the single pump provides two functions. A series of fixed restrictions are positioned in the various fluid flow lines for controlling fluid flow therethrough. These fixed restrictions may undesirably limit the flexibility of the system. Furthermore, due to the use of fixed restrictions, the relationship between the degassing negative pressure and the negative pressure at the dialyzer may undesirably change with changes in flow rates under varying operating conditions. A fluid recirculation loop is also provided downstream of the dialyzer and in cooperation with the pump for controlling the negative pressure in the dialyzer to control the flow of fluids through the system. Air from the deairing chamber will undesirably recirculate through the loop to the pump which may reduce the efficiency and life of the pump.
It is a further object of this invention to provide a single-pump-type degassing system for use in a bedside console which is flexible in that it is adaptable for use under varying conditions and in which the relationship of degassing and dialyzer pressure will not undesirably change during operation and in which the efficiency and life of the pump are maximized.
These and other objects of the invention will become apparent from the following description and appended claims.